Catalysts for the addition polymerization of unsaturated organic compounds



Patented July 31, 19 45 V dunno STATES PATENT OFFICE,

. careers-rs son zssos'zs rm: ennrnon nor-runn- IZA'I'ION. 0F, UNSA'l'UI-A'IID ORGANIC oossrormns William n. Stewart, Akron. out,

I. Company,

eorporationoi New York No Drawing. Application February Said No. 379,115

FGoodrieh adgnorto'lhe New York, N. Y...a

sooum. (OI-M3) 'lhiainventionrelatestoth'epolymerisationoi unsaturated organic compounds which are caable oi undergoing an addition m ymerimtion to form high molecular weight linear polymers, more particularly to the polymerisation 'ot coniuiated butadienes'either' alone, in mixtures with one other or with other polymerimble comonomers such asthe vinyl and vinylidene compounds. The principal object o! the invention'i's to provide a new class of catalysis or accelerators of polymer-- ization by the me c! which improved P y ers maybeobtainedinincreasedyicldandinamuch shorter interval oi time.. v I

It is known that addition may be accelerated or prom by the presence of various substances am which are oxygen and oxygen yielding compounds such as hydrogen peroxide, bensoyl peroxide, and per-salts. However, with the use oi-such known polymerisation initiators, considerable diiliculty is still experienced in obtaining high yields oi. a desirable polymer in a short interval oi time. Particularly in the commercial manufacture oi polymers by emulsion j polymerisation, the productlon schedule is hequently-disrupted by slow reactions and long in duction periods beiore the polymerisation starts. I have now discovered a large number of substances which have termed redo: systems because of their property of catalyzing or promoting oxidation reduction reactiom, particularly those occurring in biological processes, which substances are quite eil'ective in promoting addition polymerisations and which are vastly superior to any previously described noiymerimt'ion initiators or accelerators in that the polymerisation is carried out in], much shorter time, the induction period is largely eliminated, lower temperatures for the polymerization may be employed and conseouently a higher molecular weight more linear vp lymer more desirable properties is onehydrophilicgroup. Includedinthisclauoi thcblendeleeileriodic;

arealiphaticorganieccntainingthethiol (-BHLtheaulMe (-8-),01'

thedmund t-s-s-hunkssebondedbyacontaininl single valencyto an-aliphaflcradical oneor more hydrophilic substituanissuchas carsroims. am sr umhydmsm na s 'bonylgroupasulionicacidcrmmlorthelike.

Examples of such sulfurcontaining are aliphatic compoimds cuntaininl a thiol link- 8 and ph c group such as thiolactlc acid (thioslycollic acid). alpha tbiol pronionic acid (thiolactic acid), alpha .thiol hutyric acid,

alpha thiol ieobutyric monothio ethylene glycol (beta 'mercapto ethanol). beta thiol ethyl amine (beta amino ethyl mercaptan), cysteine- (beta thiol alpha amino nrwionic acid), glutathione (glutamyl cysteinyl glyeme) and the like? aliphatic compounds containing a suiiide linkage S- and an aliphatic radical containing a hydrophilic substituent such as thio dished. ethy beta hydroxy ethyl sulfide, 2-3 diamino diethyl suliide, methyl beta amino ethyl suliide, diethol gamma methyl thiol butyric acid). sugar mercaptals such as dextrose ethyl mercavtal' and many others; and compounds containing a disuliide linkage, S8, and an alinlntic radical containing a hydrophilic group such as dithio dill!- coilic acid, beta die acid. I tbeta dithio-alnha 'diaminodiiimn ll acid) and many others.

As hereinabove these sulinr eontaining compounds are eflective in promoting polymeristions whencombinedwithaheavymetalsalt. The term heavy metal as is meant to include metallicelemmts whichhave a density cystin'e' and nickel, those in subgroup B of groups I and II of'the llendeleef Periodic Table such as copper, silver, xinc, cadmium and mercury. and those in subgroup Aof groups VI and VII of the Mendeleef Periodic Table such as chromium. manganese and The class of redox systems of this invention is meant to include broadly any of the heavy metals mentimed above when combined with any of the sulfur containing compounds mentioned above of its salts rather than in the elemental state. The metal salt may be combined with the sulfur compound either as a salt or in acomplex compolmd. of uncertain chemical structure. or combinations of metallic salts with sulfur containing not known to form complexes or salts ;of a definite chemical structure may be used. In the latter event the metal may. be added as one of its simple salts while the sulfur compound may be added as such or as one of its simple salts.

The preferred redox systems are those which contain an aliphatic compound having a thiol or a disulilde linkage and also an amino, hydroxy or carboxy group, in combination with a water soluble salt of a heavy metal occurring in the 8th to 12th positions of the first long period of the periodic table such as iron, cobalt. nickel, copper and man anese. Particularly preferred are those redox systems which are known to promote or catalyse oxidation reduction reactions occurring in biolo ical processes such as heavy metal cysteine or glutathione systems.

In the pracflce of this invention monomeric compolmds or mixtures of monomers are polyamen 'insuchamannerthatthemetalispresentasone,

merized by well known methods of polymerization such as by P lymerization in homogeneous systems or bypolymerization in emulsions in pres- (awe of catalytic amolmts of the redox systems of this inyurtion. In the emulsion polymerization process which is at present preferred, the monomer or monomer mixture is emulsified in a nonsolvent liquid, usually water. with the aid of an emulsifying agent and polymerization is then effected in adding the heavy metal, sulfur containin the polymerization unsaturated organic compounds which are capable of undergoing an addition polymerisation to form a high molecular weight linear Polymer. Included in,

this class of monomers are the cml gated butadienes such as butadiene. isoprene, dimethyi butadiene, chloroprene. piperylene and the like all of which contain a om=c group; monomer mixtures of two or more of these butadienes such as a mixture of butadiene and-dimethyl butadiene; andmonomer mixtures of one or more of these conjugated butadienes with one or more other compounds which also contain a cm==c 4 group and copolymerize with mitigated butadienes such as mixtures of butadiene with vinyl compounds including aryl olefins and substituted aryl oleflns such as styrene, p-chloro styrene, pmethoxy styrene, vinyl naphthalene and the like, acrylic and methacrylic acids, esters, nitriles, and amides such as aerylicacld, acrylonitrile, methacrylonitrile, methyl acrylate, methyl methacrylate, butyl acrylate, methacrylamide and the like and other vinyl compounds such as vinyl ketones, vinyl ethersrvinyl carbaaole, vinyl furane and the like. Monomer mixtures of butadienes with other compounds containing a group such as vinylidene chloride and the like ma alsobeused. 'Allthesemonomers and monomer mixtures when polymerized or copolymerized in the manner herein form high molecular weight linear polymers. when the conlugated butadiene is the monomer or is the predominant constituent of a misnomer mixture such polymers are rubbery in character.

Other monomers or monomer mixtures which are capable of rmdergoing an addition polymerlng mi! of this invention together, if (112- siretL-wlth various other substances. the nature of whiclrwlll be described hereinafter. and agitating the emulsion until polymer is found. The resulting p ymerized emulsion containing polymer particles dispersed in a liquid medium greatly resembles natural rubber latex and may be coagulated in the usual manner to yield the soli PM The amount of the redox system to be used in polymerisation may be varied over rather wide limits provided that an excessive amount of the redox system does not inhibit or poison the polymerization reaction. For most purposes only eatalytic amounts of the redox system. say less than 2% by weight based on the weight of the monomers are preferred and in most instances the polymerizaflon proceeds, most rapidly when from .01 to 1% of the redox system is present. when the sulfur containing compound and heavy metal are added as separate compounds a mixture or about 5% of the sulfur containing compound and .l% of the heavy metal salt ispreferred. when using some heavy metals. particularl copper and manganese, however, it is desirable to use even smaller of the heavy metal salt. less than ofthisinventionmaybeusedgenerally been mentioned hereinabove; the redox v ization and which may be used in the processof this invention are the above mentioned vinyl and vinyldiene compounds as well as other vinyl compounds such as vinyl chloride and vinyl acetate,

either alone or in mixtrnes with one another, all of which polymerize toyield a linear polymer of character a thermoplastic resinous The sulfur containing -heavy metal redox systems of this invention may be used in the polymerization of m in emulsions prepared with various emulsifying agents and containing various other initiators, promoters, accelerators or modifiers of tion. As emulsifying agents, partially neutralized fatty acid soaps suchas 70-90% neutralized myristic or palmitic acids are particularly eil'ective but other well known emulsifying agents including completely neutralized fatty acid soaps such as sodium oleate and sodium palmitate and hymolal sulfates or sulfonates such as sodium lauryl sulfate and sodium isolutyl naphthalene sulfonaies may also be employed.

The redox systems containing an aliphatic sulfur containing compound of the character described and a heavy metal are preferably used to accelerate polymerizations initiated with the well known oxygen yielding such as hydrogen peroxide. organic pernxids. potassium persulfate. sodium perborate, potassium percarbonate and the like. but may'alaobemed in polytion initiators such as diazoamino benzene, trichloroacetic acid and carbon tetrachloride. They also may be used advantageousl in the polymerization of conjugated butadienes carried out in presence of a peroxide and a peroxide activator such as sodium pyrophosphate, amino acids and saturated fatty acids, orv in presence of a sub stance which is a reducing agent such as sulfur dioxide, or in presence of both an oxidizing and a reducing agent. They may also be used together with other redox systems which contain a heavy metal salt combined with other compounds including sodium pyrophosphate, levulinic acid, quebrachitol and cholesterol such as are disclosed in copending applications of William D. Stewart, Serial Nos. 379,713, 379,714, 379,716 and 379,717 filed Feb. 19, 1941. Moreover, the heavy metal, sulfur containing compounds herein disclosed may be used to effect pclymerizations carried out in the absence of any added initiator.

It is quite surprising that the sulfur containing compounds of this invention in association with a heavy -metal should promote polymerizations inasmuch as most sulfur containing compounds such as the well known natural rubber vulcanization accelerators like the thiazoles and dithiocarbamates are generally inhibitors of polymerization and other sulfur containing compounds known as polymerization modifiers such as dialkyl dixanthogens, diaryl disulfides and thiuram disulfides which increase the solubility and plasticity of the polymer usually slow down the polymerization reaction. Moreover, certain heavy metal salts when used in concentrations greater than about 0.1% also act to slow down the poly. merization. However, the redox systems of this invention containing a sulfur compound of the character described combined with a heavy metal salt, greatly accelerate the polymerization reaction. This phenomena is contrary to the normally expected result.

Although the exact manner in which the redox systems of this invention accelerate polymerizations is not known with certainty, it is believed that the redox system promotes or catalyzes an oxidation reduction reaction which oxidizes or activates the monomer molecules to such an extent that they are then capable of initiating a chain reaction which produces a linear polymer. The redox system may directly catalyze the oxidation of the monomer by an oxidizing agent such as a peroxide, if such is present, or it may be auto-oxidizable, and be capable of inducing monomer oxidation or activation by an oxidation reduction involving the redox system itself, or some other mechanism may be responsible for the increase in the rate of polymerization and for the improved properties of the polymerization products. The association of small amounts or heavy metals with various sulfur containing compounds in biological systems which undergo oxidation reduction reactions is well known and many theories have been propcunded for an explanation of such biological oxidoreductions. Since it is believed that the initiation of polymerization reactions may be quite similar to biological oxidoreduction particularly as regards the role of the redox catalyst, analogies of polymerization. systems with biological systems have proved of great value in elucidating. the action of the redox systems Of this invention. It is to be understood however that the invention is not to be limited by any proposed theory since the inclusion of the substances herein described and herein designated as redox systems in polymer- -ization mixtures greatly accelerates the process and also improves the quality of the polymerization products. i

In order to illustrate the practice of this invention and to show the accelerating effect of the redox systems herein disclosed upon polymerizations, an emulsion containing the following ingredients is prepared:

Butadiene grams 55 Acrylonitrile do 45 Hydrogen peroxide (ti solution) cc 10 Emulsifying solution (2/ aqueous solution of myristic acid neutralized with NaOH) -1 cc 250 Polymerization modifier grams 0.3

Redox system Yield Time Per cent Hour:

None (control) 98 Cobalt chloride, 0.01% Cysteine hydrochloride, .10% Cobalt chloride, 0.0l%.. Cystine, 0.10%

erric sulfate, 0.01% Jystine, 0.10%.. Zinc sulfate, 0.01%. Cystinc, 0.10% Cuprous chloride, 0.001% B-mercaptoethanol, 0.50%. Cuprous chloride, 0.001%. Glutathione, 0.50% Nickel sulfate, 01%.... B-mercaptoethanol, .50% Mcrcuric chloride, .0l% B-mcrcaptoethanol, .50%

of polymerization is measured by determining the percent yield at various intervals during the process. The accelerating effect of the redox system is shown below:

For Per- Per- Pcr- Per- 03 *ii *ii "13 we yie yie yie yield Redo) System after after after after after 7% 10% 12% 23 45 hrs. hrs. hrs. hrs. hrs.

l; 1'one(control) 0 0 0 45 94 errous ammonium. guliate, 0.05% (c0ntrol)n. 0 7 38 93 crrous ammonium su ate, (1.05, FGlutathione, .50%.. ..1 f. m 83 93 errous ammonium su ate, 0.05 22 diamino diethyl sulfide, 0.509;. 4g 85 92 Ferrous ammonium sulfate, 0.05%. 66 B9 93 Cysteine hydrochloride, 0.50%.. Ferrous ammonium sulfate, 0.05%. Dieggl dithiosulio succinate, 71 93 0. 0 Ferrous ammonium sulfate- 0.057 B-mercaptoethanol,.0.50% 76 90 94 The table shows that withv the redox systems of this invention polymerization is substantially complete in 12% hrs. while with no redox system 45 hrs. is required and with a heavy metal salt alon'e23. hrs. is required; Other embodiments of the invention in which-various other redox systems are used with various other monomers and monomer mixtures, catalysts and emulsifying agents also show that the polymerization velocity is increased by the practiceof this invention.

In the practice of theinvention it is sometimes desirable to add various substances other than terns which are very effective incatalyzing bithose mentioned above to the polymerization recipe. For example when employing redox sysological exodoreduction reactions such as the glutathione-heavy metal system it may be desirable to add colloids which are usually present in biological systems as carriers for the redox system such as proteins, polypeptides, peptides, or

other colloidal material. It may also be desirable to add materials which influence the quality of the finished polymer such as plasticizing or stabilizing agents for the polymer.

The practice of this invention also allows polymerizations to proceed rapidly under conditions where-polymerization would ordinarily be impossible, because the great accelerating effect of will be obvious to those skilled in the art that many modifications and variations are within the spirit and scope of the invention as defined by the appended claims.

I claim:

1. The method which comprises subjecting a polymerizable material consisting of at least one unsaturated organic compound which contains a roup and which undergoes in aqueous emulsion an addition polymerization to form a high molecular weight linear polymer, to polymerization in aqueous emulsion in the presence of a catalyst comprising a water-soluble heavy metal salt combined with an aliphatic organic compound containing at least one but not more than two divalent sulfur atoms each of which is connected by its two valences to two different atoms, and having at least one of said sulfur atoms connected by at least one of 'its two valences to an aliphatic radical containing at least one hydrophilic group, the total concentration of the heavy metal salt and the said aliphatic organic compound being less than 2% by weight of the material polymerized, and the concentration of the heavy metal salt being such that the polymerization proceeds more rapidly than in the absence of the heavy metal salt. v i

2. The method of claim 1 in which the material subjected to polymerization is a polymerizable conjugated butadiene.

3. The method of claim 1 in which the material subjected to polymerization is a mixture of a polymeriz'able coniugated-butadiene and at least one other compound-which intains a Ch 0 t h a a group and is copolymerizable therewith in aqueous emulsion. i

4. The method which comprises subjecting a mixture of a polymerizable conjugated butadiene and at least one other compound which contains a groupand is copolymerizable therewith in aqueous emulsion, to ,polymerizationlin aqueous emulsion in the presence of a catalyst comprising a water soluble heavy metal salt combined with an aliphatic organic compound containing a single divalent sulfur .atom connected by one of. its valences to a hydrogen atom and by the other of its valences to an aliphatic radical containing at least one hydrophilic group, the total concentration of the heavy metal salt and the said aliphatic tion of the heavy metal salt being such that the, polymerization proceeds more rapidly than in the absence of the heavy metal salt.

5. The method of claim 4(in which the heavy metal salt is a salt'wof a heavymetal occurring in the 6th to 12th positions of the first long period of the periodic. table.

6. The method of claim 4 in which the heavy metal salt is a salt of aheavy metal occurring in the 6th to 12th positions ofthe first long period of the periodic table; and the aliphatic organic compound is an hydroxy-substituted aliphatic mercaptan.

7. The method of claim 4 in which the material 0 polymerized is a mixture of butadiene-1,3 and at least one copolymerizable vinyl compound the heavy metal salt is a salt of a heavy metal occurring in groupVIII'and the first long period of the periodic table; and the aliphatic organic compound is an hydroxy-substituted aliphatic mercaptan. I 8. The method of claim 4 in which the'material polymerized is amixture of butadlene-1,3 and at least one copolymerizablevinyl compound; the heavy metal salt is a salt of a heavy metal occurring in group VIII and the first longperiod of the periodic table; and the aliphatic organic compound is beta-mercapto ethanol. 9. Themethod of claim 4 in which the material polymerized is a mixture of butadiene-1,3 and mixture of a polymerizable conjugated butadiene and at least one othercompound which contains a CHFC/ I group and is copolymerizable' therewith in aqueous emulsion, to polymerization in aqueous emul sion in the presence of a catalyst comprising. a. water-soluble heavy metal salt combinedwith an aliphatic organic 'compoundcontaining a single divalent sulfur atom connected byvone of its valences to a hydrogen atom and by the other of its valences to an aliphatic radical containing at least one amino group and at least one carboxy group. the total concentration of the heavy metal salt and the aliphatic organic compound being less than 2% by weight of the material polymerized and the concentration of the heavy metal salt being such that the polymerization proceeds more rapidly than in the absence of the heavy metal salt.

11. The method of claim in which the material polymerized is a mixture of butadiene-1,3 and a copolymerizable vinyl compound; and the heavy metal salt is a salt of a heavy metal occurring in the 6th to 12th positions of the first long period of the periodic table.

12. The method of claim 10 in which the material polymerized is a mixture of butadiene-1,3 and a copolymerizable vinyl compound; the heavy metal salt is a salt of a heavy metal occurring in the 6th to 12th positions of the first long Pe od of the periodic table; and the aliphatic organic compound is glutathione.

13. The method of claim 10 in which the material polymerized is a mixture of butadiene-1,3 and acrylonitrile; and the catalyst comprises glutathione and a water soluble copper salt.

14. The method which comprises subjecting a mixture of a polymerizable conjugated butadiene and at least one other compound which contains a group and is copolymerizable therewith in aqueous emulsion, to polymerization in aqueous emulsion in the presence of a catalyst comprising a water soluble heavy metal salt combined with an allphatic organic compound of the formula wherein X is an aliphatic radical containing at least one hydrophilic group, the total concentration of the heavy metal salt and the aliphatic organic compound being less than 2% by weight of the material polymerized and the concentration of the heavy metalsalt being such that the polymerization proceeds more rapidly than in the absence of the heavy metal salt.

15. The method of claim 14 in which the heavy metal salt is a salt of a heavy metal occun'lng in the 6th to 12th positions of the first long period oi the periodic table; and the aliphatic organic compound is a compound of the formula ZBBX Certificate Patent No. 2,380,475.

wherein x is an aliphatic radical containing a carboxy group.

16. The method of claim 14 in which the heavy metal salt is a salt of a heavy metal occurring in the 6th to 12th positions of the first long period of the periodic table; and the aliphatic organic compound is a compound of the formula wherein X is an aliphatic radical containing at least one carboxy group and at least one amino group.

17. The method of claim 14 in which the material polymerized is a mixture of butadiene-1,3 and a. copolymerizable vinyl compound; the heavy metal salt is a salt of a heavy metal occurring in group VIII and the first long period of the periodic table; and the aliphatic organic compound is cystine.

18. The method of claim 14 in which the material polymerized is a mixture of butadiene-l,3 and acrylonitrile and the catalyst comprises cystine and a water soluble iron salt.

19. The method which comprises subjecting a mixture oi. a polymerizable conjugated butadiene and at least one other compound which contains a group and is copolymerizable therewith in aqueous emulsion, to polymerization in aqueous emulsion in the presence of a catalyst comprising a complex compound of a heavy metal and an aliphatic organic compound containing at least one but not more than two divalent sulfur atoms and havin at least one of said sulfur atoms connected by a single valence to an aliphatic radical containing at least one hydrophilic group, the concentration of the complex compound being less than 2% by weight of the material polymerized and such that the polymerization proceeds more rapidly than in the absence of the complex compound.

20. The method of claim 19 in which the heavy metal is a metal occurring in the 6th to 12th positions of the first long period of the periodic table.

WE-LIAM D. S'I'E'WART.

Correction July 31, 1945.

WILLIAM D. STEWART It is hereby certified that error appears in the numbered patent requiring correction as follows: for thiolactic read th'iolacetic; and that the said Letters Patent should rinted specification of the above i 'age 1, second column, line 10 be read with this correction therein that the same may conform to the record of the case in the Patent Ofiice.

Signed and sealed this 4th day of June, A. D. 1946.

LESLIEFRAZEB,

FirstZAseistant Gommiuiomr of Patents.

ing such that the polymerization proceeds more rapidly than in the absence of the heavy metal salt.

11. The method of claim in which the material polymerized is a mixture of butadiene-1,3 and a copolymerizable vinyl compound; and the heavy metal salt is a salt of a heavy metal occurring in the 6th to 12th positions of the first long period of the periodic table.

12. The method of claim 10 in which the material polymerized is a mixture of butadiene-1,3 and a copolymerizable vinyl compound; the heavy metal salt is a salt of a heavy metal occurring in the 6th to 12th positions of the first long Pe od of the periodic table; and the aliphatic organic compound is glutathione.

13. The method of claim 10 in which the material polymerized is a mixture of butadiene-1,3 and acrylonitrile; and the catalyst comprises glutathione and a water soluble copper salt.

14. The method which comprises subjecting a mixture of a polymerizable conjugated butadiene and at least one other compound which contains a group and is copolymerizable therewith in aqueous emulsion, to polymerization in aqueous emulsion in the presence of a catalyst comprising a water soluble heavy metal salt combined with an allphatic organic compound of the formula wherein X is an aliphatic radical containing at least one hydrophilic group, the total concentration of the heavy metal salt and the aliphatic organic compound being less than 2% by weight of the material polymerized and the concentration of the heavy metalsalt being such that the polymerization proceeds more rapidly than in the absence of the heavy metal salt.

15. The method of claim 14 in which the heavy metal salt is a salt of a heavy metal occun'lng in the 6th to 12th positions of the first long period oi the periodic table; and the aliphatic organic compound is a compound of the formula ZBBX Certificate Patent No. 2,380,475.

wherein x is an aliphatic radical containing a carboxy group.

16. The method of claim 14 in which the heavy metal salt is a salt of a heavy metal occurring in the 6th to 12th positions of the first long period of the periodic table; and the aliphatic organic compound is a compound of the formula wherein X is an aliphatic radical containing at least one carboxy group and at least one amino group.

17. The method of claim 14 in which the material polymerized is a mixture of butadiene-1,3 and a. copolymerizable vinyl compound; the heavy metal salt is a salt of a heavy metal occurring in group VIII and the first long period of the periodic table; and the aliphatic organic compound is cystine.

18. The method of claim 14 in which the material polymerized is a mixture of butadiene-l,3 and acrylonitrile and the catalyst comprises cystine and a water soluble iron salt.

19. The method which comprises subjecting a mixture oi. a polymerizable conjugated butadiene and at least one other compound which contains a group and is copolymerizable therewith in aqueous emulsion, to polymerization in aqueous emulsion in the presence of a catalyst comprising a complex compound of a heavy metal and an aliphatic organic compound containing at least one but not more than two divalent sulfur atoms and havin at least one of said sulfur atoms connected by a single valence to an aliphatic radical containing at least one hydrophilic group, the concentration of the complex compound being less than 2% by weight of the material polymerized and such that the polymerization proceeds more rapidly than in the absence of the complex compound.

20. The method of claim 19 in which the heavy metal is a metal occurring in the 6th to 12th positions of the first long period of the periodic table.

WE-LIAM D. S'I'E'WART.

Correction July 31, 1945.

WILLIAM D. STEWART It is hereby certified that error appears in the numbered patent requiring correction as follows: for thiolactic read th'iolacetic; and that the said Letters Patent should rinted specification of the above i 'age 1, second column, line 10 be read with this correction therein that the same may conform to the record of the case in the Patent Ofiice.

Signed and sealed this 4th day of June, A. D. 1946.

LESLIEFRAZEB,

FirstZAseistant Gommiuiomr of Patents. 

